Citation:
Abstract:
We explore the connection between different classes of active galacticnuclei (AGNs) and the evolution of their host galaxies, by deriving hostgalaxy properties, clustering, and Eddington ratios of AGNs selected inthe radio, X-ray, and infrared (IR) wavebands. We study a sample of 585AGNs at 0.25 < z < 0.8 using redshifts from the AGN and GalaxyEvolution Survey (AGES). We select AGNs with observations in the radioat 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays fromthe Chandra XBoötes Survey, and mid-IR from the Spitzer IRACShallow Survey. The radio, X-ray, and IR AGN samples show only modestoverlap, indicating that to the flux limits of the survey, theyrepresent largely distinct classes of AGNs. We derive host galaxy colorsand luminosities, as well as Eddington ratios, for obscured or opticallyfaint AGNs. We also measure the two-point cross-correlation between AGNsand galaxies on scales of 0.3-10 h -1 Mpc, and derive typicaldark matter halo masses. We find that: (1) radio AGNs are mainly foundin luminous red sequence galaxies, are strongly clustered (with Mhalo ~ 3 × 1013 h -1 Msun), and have very low Eddington ratios λ lsim10-3 (2) X-ray-selected AGNs are preferentially found ingalaxies that lie in the "green valley" of color-magnitude space and areclustered similar to the typical AGES galaxies (M halo ~1013 h -1 M sun), with 10-3lsim λ lsim 1; (3) IR AGNs reside in slightly bluer, slightlyless luminous galaxies than X-ray AGNs, are weakly clustered (Mhalo lsim 1012 h -1 M sun),and have λ>10-2. We interpret these results interms of a simple model of AGN and galaxy evolution, whereby a "quasar"phase and the growth of the stellar bulge occurs when a galaxy's darkmatter halo reaches a critical mass between ~1012 and1013 M sun. After this event, star formationceases and AGN accretion shifts from radiatively efficient (optical- andIR-bright) to radiatively inefficient (optically faint, radio-bright)modes.